The decision from the Economic Community of West African States came after Burkina Faso, Mali and Niger reaffirmed as "irreversible" their decision to quit the group, which they condemned as subservient to ex-colonial ruler France.
The imminent departure of the three Sahel states could have a major impact on free trade and movement as well as on security cooperation in a region where jihadists tied both to Al Qaeda and Islamic State are gaining ground.
The departure of Mali, Burkina Faso and Niger would have become effective next month, one year after their initial January 2024 announcements, according to the bloc's regulations.
"The authority decides to set the period from 29 January, 2025, to 29 July, 2025, as a transitional period and to keep ECOWAS doors open to the three countries," the group said in a statement following a meeting of West African leaders in Abuja.
Among those attending the summit was Senegal's President Bassirou Diomaye Faye, appointed as a mediator with the breakaway states by the 15-member ECOWAS in July.
Faye said last week he was "making progress" in talks with the three and said there was no reason for them not to maintain relations, especially given the security situation.
Togo's President Faure Gnassingbe has also been mediating with the Sahel states.
ECOWAS on Sunday authorised both presidents to continue their negotiations with the three states.
The three breakaways have also formed their own confederation, the Alliance of Sahel States (AES), after severing ties with France, and pivoting towards Russia.
The three did not announce plans to attend the Abuja summit, but they held a separate ministerial-level meeting Friday in Niger's capital, Niamey.
"The ministers reiterate the irreversible decision to withdraw from ECOWAS and are committed to pursuing a process of reflection on the means of exiting in the best interests of their peoples," they said in a joint statement.
The three states have all gone through military coups and jihadist insurgencies in recent years. ECOWAS member state Guinea is also run by a military government after a 2021 coup.
Tensions with ECOWAS spiked after the group threatened a military intervention over a July 2023 coup in Niger -- the region's sixth in three years -- and imposed heavy sanctions on the country.
That position has since softened, though ECOWAS states are split over the best course of action to deal with the military governments.
In March, ECOWAS lifted some of the sanctions imposed on Niger in a bid to restart dialogue, especially over the fate of deposed President Mohamed Bazoum, who has been detained since the coup.
Earlier this year, Nigeria's top military commander met Niger's army chief to strengthen security cooperation, especially communication between the two militaries and participation in a multi-national task force along the border area.
